My pair that came in had a problem with the right cup not putting out as much sound.
Turns out, after I opened them up, one of the little felt bass-reducing pads on it was covering the hole completely.
After taking the felt off itself, I saw that the sticky silicone-like stuff had formed a complete seal over the hole.
But I fixed it (removed it and replaced with my own material) and it sounds perfectly balanced now. Great sounding cans, super comfortable - the band on the top pulls at my hair a little bit though, not too bad however. May try experimenting with different foams for different sound...